Electric discharge tube



Dec. 7, 1937.

w. DALLENBACH ELECTRIC DISCHARGE TUBE Filed Sept. 27, 1935 //7 11817 for:

J 1N6 C M% M much AOQ "a D a U m W 1|? August 13, 1934) of the same inventor, to smaller Patented Dec. 7, 1937 PATENT oe-1c ELECTRIC DISCHARGE TUBE Walter Dallenbach, Berlin-Charlottenburg, Germany, assignor to N. V. Machinerieen-en Apparaten Fabrieken Meaf, Utrecht, Netherlands Application September 27, 1935, Serial No. 42,498 In Germany October 5, 1934 10 Claims.

This invention relates to electric discharge tubes with a filling of rarefied gas or vapour and an arc-like discharge, such as are used for producing light, for the limitation of currents, for

I the generation of oscillations and the like.

In these discharge tubes with an arc-like discharge, it can be observed, that with a current strength increasing the voltage drop across the whole tube first decreases and then, with very great strength of current, increases again. The inventor has ascertained, that this increase of the voltage drop may be shifted, as already embodied in the two applications Serial No. 650,572 (filed January 6, 1933) and Serial No. 739,678 (filed strengths of current, by separating the anode or the anode space from the remainder of the discharge space by a diaphragm-like partition. The discharge is forced to pass through the dia- 1 phragm-like opening of this partition, thereby being constricted to such an extent, that an impoverishment in positive ions in the anode space will take place. During the passage of current through thetube the electrons, issuing from the 26,- cathode, travel towards the anode, but the positive ions, produced there, travel in the opposite direction from the anode to the cathode. Since a fresh supply of positive ions from the surface of the anode is not coming forth, the density of the positive ions in the anode space, closed up by the partition, is no longer suflicient for the compensation of the electron space charge. In consequence thereof, the voltage-current-characteristic rises.

In the applications of the inventor previously mentioned, it has already been stated what advantages will be attained by said rise of the voltage drop in these arc-discharge tubes; For example, it will be possible to produce by means of these tubes high frequency oscillations of a very great strength, to use them as current limiters or,

furthermore, for producing light etc.

The present invention aims at improving these discharge tubes containing a diaphragm-like pair'- tition disposed between cathode and anode, so that they are working absolutely reliably and that they are protected from are ignitions at the partition. In consideration of the fact, that the partition is situated immediately in the discharge gap and restricts the discharge, it is the edges of the openings of the diaphragm o-r partition, which will be subject to a most violent bombardment of charge carriers, ions and electrons. The partition will, in consequence, be heated most excessively and may, by becoming self-emitting, give rise to are ignitions towards one of the main electrodes.

The chief object of the present invention is, for the purpose of obviating these drawbacks, to improve the diaphragm like partition, by causing the latter to consist of a plurality of single partitions being arranged in series, 1-. e. one after the other, through the openings of which thedischarge has to pass successively on its way from cathode to anode.

It is within the limits of the present invention that the openings of the diaphragm or partition, are approximately equal in size to the mean, free' length of path of the particles of the gas or va-' pour content. i

A further object of the present invention is to make the diaphragms or partitions from metal and to dispose them closely in series or one behind the other, insulated from each other.

Further characteristic features will become apparent from the following specification and the accompanying drawing. Fig. 1 represents the construction of such a tube with an are or an arclike discharge in accordance with the present invention, containing a mercury cathode and an auxiliary ignition electrode. Figs. 2 to 4 illustrate several further examples of performance of the diaphragm-like partition in accordance with the present invention. I

The discharge tube in accordance with Fig. 1 consists of the glass bulb l, the cathode 2 and the anode 3. In the discharge gap between thesetwo electrodes the two diaphragms or partitions 5 and 6 have been provided. It is, as a matter of course, perfectly within the limits of the present invention, to use not only two, but also three and more separate diaphragms or partitions. The diaphragms or partitions 5 and 6 of the example of performance represented in the accompanying drawing are of pot-like shape and are each provided with one opening only. The inner diaphragm 5 closely joins with its edge a collar I of the glass bulb. Between the inner and the outer diaphragm a ring 8, consisting of a suitable insulating material, has been deposited. Instead of-using a pot-shaped partition also such of disk-shape may be used, the edges of which are then terminating approximately with the neck of the glass bulb.

If the discharge tube is supplied with increas ing current intensity, the latter will soon become saturated. The saturation value is obtained approximately in the following manner:

In the opening of the screen there is formed a so-called striction cathode which all electrons,

vacuum transmitter valves or power tubes.

emitted by the cathode, have to pass. At this point there exists a fixed relation between the electron current passing from the cathode to the anode and the positive ion current passing in the opposite direction. Since the chamber formed by the diaphragms or partitions 5, 6 excludes the anode from the remaining part of the discharge gap, an impoverishment in positive ions soon takes place here in consequence of the permanent temperature movement of the neutral gas orv vapour mercury atoms. As long as the number of atoms diffusing through the openings into the discharge gap within the anode space will be constant per unit time, the saturation value of the current of the tube will then also be constant.

The electron current, passing through the striction cathode formed by the opening of the screen, flows through the space towards the anode in the form of a regular beam. The striction cathode thus acts in the anode space as a novel cathode (plasma cathode). for it is fed by the irregularly moving electrons of the plasma in the cathode space. In consequence of the extraordinarily great strength of current, being possible in a gas discharge, it will be possible to attain by means of this plasma cathode also current densities exceeding by far the current densities of the usual cathodes. For this reason, these tubes will render it possible, say in the case of production of high-frequency oscillations, to ensure considerably greater-efiects than with the usual high For the same reasons the new tube will also prove most advantageousparticularly as light source or current limiting tube.

The prevention of arc ignitions at the diaphragm-like partition in consequence of excessive ion or electron bombardments, is secured, by forming the partition of a plurality of separate diaphragms 5, 6, Fig. 1 approximately in the following manner:

The outer diaphragm -6 of the anode space takes in the discharge gap a certain potential which is identical with that which would prevail, if this diaphragm would 'be there by itself. The

potential of the diaphragm 5, however, approaches more closely the anode potential. The positive ions of the anode space, therefore, strike this diaphragm 5 at a lower speed than the partition 6, the latter being protected from an excessive ion bombardment and thus from excessive heating.

The tube illustrated in Fig. 1 is provided with a mercury cathode.- The same effect could be procured with the aid of a hot cathode tube. For the purpose of securing in the proximity of the diaphragm and anode a mercury vapour pressure of the greatest possible uniformity, it is advisable, to provide above the mercury cathode 2 a screen 9. The screen may simultaneously be made to serve as auxiliary anode for maintaining the exciting arc. In order to start the discharge from the anode to the cathode without using a special auxiliary cathode, it is advisable to connect the diaphragm or partition 5; 6 with the anode potential through a resistance. As soon as the anode takes positive voltage, an electron through the resistance 4.

The openings of the different diaphragms or partitions may be of difierent size, causing difierent effects to be attained. It will be advisable, as indicated in Fig. 2, to cause the opening of the inner diaphragm or partition to be somewhat smaller than thaat of the outer one. If, however, the openings are made of uniform size or even, as shown in Fig. 3, if those of the outer diaphragm or partition are made smaller than those of the inner one, there may be a risk, as indicated by the arrows in Fig. 3, that the positive ions excessively bombard the edges of the outer opening, so that at that point are ignitions can easily be caused. If, on the other hand, the outer opening is made too large relatively to the inner one, the inner diaphragm or partition, particularly :its edges (vide the arrows in Fig. 2) will be bombarded by electrons, causing a heating of the edges of the screen and an approximation of the potential of the inner diaphragm to that of the cathode.

The diaphragms or partitions may also be provided with openings as shown in Fig. 4. The latter further illustrates the fact, that between the two bottoms of the diaphragms or partitions insulating material has been provided. The walls of the small openings in the insulating material are'taking an irregular course, rendering, in accordance with the kinetic gas theory, the admission of neutral particles into the anode space more diflicult.

In accordance with Fig. 1 the space between the diaphragms or partitions decreases towards the opening. This will cause the electron current in the space between the diaphragms or partitions to be reduced. The distance between the edges of the diaphragms or partitions must not, however, be too short either, because otherwise are ignitions from diaphragm to diaphragm will take place.

If the tube in accordance with the present invention is used for the production of short waves for which, as has been ascertained by experiments, it is particularly adapted, it is especially advisable to provide a number of diaphragms or partitions, but at least two diaphragms or partitions, because the ion bombardment in 'connection with these rapid oscillations is particularly violent.

It is a matter of course, that the present in-- vention is not limited to the represented example of performance, but may be applied to all tubes, in which the danger of an ignition between an electrode and a diaphragm or partition presents itself.

What I claim, is:

1. An electric discharge tube for the production of high frequency oscillations comprising a closed vessel, an anode, a cathode, an ionizable medium of sumcient pressure to maintain an arc-like discharge between said electrodes when potentials are applied to the latter, a plurality of walls slightly spaced from each other and being' of the mean free path lengths of the particles of said medium, whereby the discharge path through said-openings is constricted to a cross sectioncorresponding to the order of the magnitude of the mean free path of the particles in the ionizable medium and the prevailing current density of said discharge adjacent said openings causes an ion paucity whereby the potential drop in the vessel increaseswith increase of current.

2. An electric discharge tube for the production of high frequency oscillations comprising a closed vessel, an anode, a cathode, an ionizable medium of sufficient pressure to maintain an arc-like discharge between said electrodes when potentials are applied to the latter, two metallic walls slightly spaced from each other and being disposed between the electrodes and having aligned openings therein, each of said openings having a diameter approximately equal to the magnitude of the mean free path lengths of the particles of said medium, whereby the discharge path through said openings is constricted to a cross section corresponding to the order of the magnitude of the mean free path of the particles in the ionizable medium and the prevailing current density of said discharge adjacent said openings causes an ion paucity whereby the potential drop in the vessel increases with increase of current.

3. An electric discharge tube for the production of high frequency oscillations comprising a closed vessel, an anode, a cathode, an ionizable medium of suflicient pressure to maintain an arclike discharge between said electrodes when potentials are applied to the latter, a plurality of walls slightly spaced from each other and being disposed between the electrodes and having aligned openings therein, the space between said walls decreasing progressively adjacent said openings, each of said openings having a diameter of the order of the magnitude of the mean free path lengths of the particles in said medium, whereby the discharge path through said openings is constricted to a cross section corresponding to the order of the magnitude of the mean free path of the particles in the ionizable medium and the prevailing current density of said discharge adjacent said openings causes an ion paucity whereby the potential drop in the vessel increases with increase of current.

4. An electric discharge tube for the production of high frequency oscillations comprising a closed vessel, an anode, a cathode, an ionizable medium of sufficient pressure to maintain an arelike discharge between said electrodes when potentials are applied to the latter, a plurality of metallic walls slightly spaced from each other and being disposed between the electrodes and aligned openings therein, electrical insulating material between each of said metallic walls, said openings having a diameter approximately equal to the magnitude of the mean free path lengths of the particles of said medium, whereby the discharge path through said openings is constricted to a cross section corresponding to the order of the magnitude of the mean free path of the particles in the ionizable medium and the prevailing current density of said discharge adjacent said openings causes an ion paucity whereby the potential drop in the vessel increases with increase of current.

5. An electric discharge tube for the production of high frequency oscillations comprising a closed vessel, an anode, a cathode, an ionizable medium of sufiicient pressure to maintain an arelike discharge between said electrodes when potentials are applied to the latter, a plurality of walls slightly spaced from each other and being disposed between the electrodes and having aligned openings therein, the openings varying slightly in size and each having a diameter of the order of the magnitude of the mean free path lengths of the particles in said medium, wherebythe discharge path through saidopenings is constricted to a cross section corresponding to the order of the magnitude of the mean free path of the particles in the ionizable medium and the prevailing current density of said discharge adjacent said openings causes an ion paucity whereby the potential drop in the vessel increases with increase of current.

6. An electric discharge tube for the production of high frequency oscillations as claimed in claim 5, the wall nearest the anode having the smaller opening therein.

'7. An electric discharge tube for the production of high frequency oscillations comprising a closed vessel, an anode, a cathode, an ionizable medium of sufficient pressure to maintain an arelike discharge between said electrodes when potentials are applied to the latter, a plurality of electrically conductive walls slightly spaced from each other and being disposed between the electrodes and having a plurality of aligned openings therein, insulating material between said walls having passages aligned with said openings, each of said openings and said passages having a diameter of the order of the magnitude of the mean free path lengths of the particles in said medium, whereby the discharge path through said openings is constricted to a cross section corresponding to the order of the magnitude of the'mean free path of the particles in the ionizable medium and the prevailing current density of said discharge adjacent said openings causes anion paucity whereby the potential dropin the vessel increases with increase of current.

8. An electric discharge tube for the production of high frequency oscillations as claimed in claim '7, the passages through the insulating material being tortuous.

9. An electric discharge tube for the production of high frequency oscillations comprising a closed vessel, an anode, a cathode, an ionizable medium of sufiicient pressure to maintain an arclike discharge between said electrodes when potentials are applied to the latter, a plurality of electrically conductive walls insulated from each other and having aligned openings therein and being disposed between the electrodes, a lead extending from at least one of said walls adapted to be connected to the control potential, each of said openings having a diameter of the order of the magnitude of the mean free path lengths of the particles in said medium, whereby the discharge path through said openings is constricted to a cross section corresponding to the order of the magnitude of the mean free path of the particles in the ionizable medium and the prevailing current density of said discharge adjacent said openings causes an ion paucity whereby the potential drop in the vessel increases with increase of current.

10. An electric discharge tube for the production of high frequency oscillations comprising a closed vessel, an anode, a cathode, an ionizable medium of sufficient pressure to maintain an arclike discharge between said electrodes when potentials are applied to the latter, a plurality of electrically conductive Walls slightly spaced from iii) said openings is constricted to a cross section corresponding to the order of the magnitude of the mean free path of the particles in the ionizable medium and the prevailing current density of said discharge adjacent said openings causes an ion paucity whereby the potential drop in the vessel increases with increase of current.

WALTER DALLENBACH- 

